The present invention is related to an improved catalytic composition and an alkylation or transalkylation process embodying that catalytic composition. More particularly, this invention involves an alkylation or transalkylation catalyst composition comprising a hydrogen form crystalline aluminosilicate zeolite and a refractory inorganic oxide.
The alkylation or transalkylation of aromatics are processes well known for their ability to produce such monoalkylaromatic products as ethylbenzene, cumene, linear alkylbenzenes, and so forth. Such monoalkylaromatic compounds are important chemical precursors in the production of detergents and polymers among others. Alkylation catalysts that are known to produce alkylaromatic compounds include the well-known Friedel-Crafts catalysts: sulfuric acid, phosphoric acid, hydrofluoric acid, and aluminum chloride in either liquid or solid supported form. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized as alkylating reactants in both a modified and naturally occurring form.
A myriad of processing schemes employing an alkylation reaction zone and/or a transalkylation reaction zone are well known to produce monoalkylaromatic products in high yields. One drawback concerning existing alkylation/transalkylation processes is the potential for the alkylatio and/or the transalkylation catalyst to produce undesirable products such as alkylating agent oligomers, heavy polyaromatic compounds, and unwanted monoalkylaromatics. The alkylating agent oligomers can be especially troublesome as they are often recovered with the desired monoalkylaromatic product where they can detrimentally affect the utility of the monoalkylaromatic product in further conversion processes. An example of this would be the contamination of cumene with propylene oligomers which may reduce the utility of using such contaminated cumene as a phenol process feedstock and ultimately for the production of phenolic resins due to the presence of the oligomers as an inert compound within the cross-linked resins.
Another drawback inherent to some existing alkylation/transalkylation reaction zone containing processes is the use of Friedel-Crafts catalysts such as solid phosphoric acid or hydrofluoric acid as the alkylation and/or transalkylation catalyst. Many of these catalysts require a water cofeed and produce an extremely corrosive sludge by-product. The utilization of such sludge-producing catalysts in an alkylation process requires that special design considerations be made regarding unit metallurgy, safety, and by-product neutralization. Such design considerations are typically costly and may add significantly to the construction and operations costs of such processes. Additionally, the use of Friedel-Crafts catalyst requires a once-through processing scheme to ensure that damaging corrosive materials are not recycled into the reaction zone. This requirement necessitates the operation of the process at high conversion conditions which tend to produce greater amounts of unwanted by-products such as alkylating agent oligomers and heavy by-products.
More recently, crystalline aluminosilicate zeolites which have shown catalytic activity have been effectively used in the alkylation and transalkylation of aromatics. Both natural and synthetic crystalline aluminosilicates have been employed. Included among these are the Type X and Type Y zeolites as well as synthetic mordenite.
Specifically, the zeolites known as mordenites have received great attention. Mordenites are crystalline natural or synthetic zeolites of the aluminosilicate type; generally, they have a composition expressed in moles of oxide of EQU 1.0.+-.0.2Na.sub.2 O.Al.sub.2 O.sub.3.10.+-.0.5SiO.sub.2 ;
the quantity of SiO.sub.2 may also be larger. Instead of all or part of the sodium, other alkali metals and/or alkaline earth metals may be present.
In general, it has been found that the sodium form of mordenite is not particularly effective for the alkylation or transalkylation of hydrocarbons and that replacing all, or for the greater part, of the sodium cations with hydrogen ions yields the more advantageous hydrogen form mordenite. Conversion of the sodium form to the hydrogen form can be accomplished by a number of means. One method is the direct replacement of sodium ions with hydrogen ions using an acidified aqueous solution where the process of ion exchange is employed. Another method involves substitution of the sodium ions with ammonium ions followed by decomposition of the ammonium form using a high temperature oxidative treatment.
The activity and selectivity of alkylation or transalkylation catalysts depend on a variety of factors, such as the mode of catalyst preparation, the presence or absence of promoters, quality of raw materials, feedstock quality, process conditions, and the like. Suitable catalysts can be conventionally prepared by combining commercially available crystalline zeolites, such as, a hydrogen form mordenite, with a suitable matrix material. A new catalyst has now been discovered which exhibits greatly improved alkylation and transalkylation performance when compared to conventionally prepared catalysts.